Heretofore, there has been known a vehicle suspension apparatus which comprises: a single piece of pipe member formed in a U shape in top plan view; a coupling member (cross member) coupling together right and left side portions of the U-shaped pipe member; and transfer means composed of two pipe members disposed in an inverted V shape with respect to the U-shaped pipe member, as disclosed in the following Patent Document 1. This vehicle suspension apparatus is configured to transfer an external force input from a suspension arm into a front subframe, to a mounting portion provided on a vehicle body-side member via the transfer means, thereby increasing a suspension arm mounting rigidity and improve a torsional rigidity of the apparatus.
There has also been known a vehicle lower body structure which comprises a front subframe (suspension member) capable of transferring a collision load input from a front end toward a rear end of a vehicle, as disclosed in the following Patent Document 2. This front subframe has a rear portion joined to a pair of right and left floor frames (side members) and a pair of right and left tunnel reinforcements of a vehicle body at four points arranged in a vehicle width direction. Thus, even in a situation where a frontal collision load input from the front end of the vehicle is concentrated on one side in the vehicle width direction, it becomes possible to transfer the frontal collision load to front and rear frameworks of a lower portion of the vehicle body in an adequately distributed manner.
Further, there has been a vehicle front body structure which comprises: a front subframe located beneath a vehicle front-side portion of a vehicle-body frame, wherein a front end thereof extends up to a vicinity of a front end of the vehicle front-side portion of the vehicle-body frame; and a floor panel formed over a periphery on a lower side of a passenger compartment, and provided with a pair of right and left mounting portions each configured to be fastened to a respective one of right and left rear end-side support portions provided close to a rear end of the front subframe, and a stopper portion formed to protrude downwardly with respect to the floor panel at a position rearward of each of the mounting portions, wherein each of the mounting portions and the stopper portion is formed in the vicinity of a front end of the floor panel, as disclosed in the following Patent Document 3. In this vehicle front body structure, the floor panel comprises a floor frame provided to extend in a front-rear direction of the vehicle, and a branch frame provided to branch from a branch site located in a front portion of the floor frame, toward a vehicle inward side and extend rearwardly, wherein each of the floor frame and the branch frame is formed to protrude downwardly along the extending direction. Further, at or in a vicinity of the branch site, each of the mounting portions is formed such that a height position of a lower surface thereof is higher than that of a lower surface of the floor frame in a vicinity of the mounting portion, and, at or in the vicinity of the branch site, the stopper portion is formed in adjacent relation to the floor frame.
The vehicle suspension apparatus disclosed in the Patent Document 1 is configured to transfer an external force such as a lateral force input from the suspension arm into the front subframe during vehicle traveling, to the mounting portion provided on the vehicle body-side high-rigidity member (floor frame), so that it becomes possible to stably support an external force given from the suspension arm to the front subframe, and improve a supporting rigidity for a front arm pivotally supported by the front subframe. However, in this vehicle suspension apparatus, the U-shaped pipe member making up a main body of the front subframe has to be increased in diameter in order to satisfactorily ensure the torsional rigidity and the like, wall thickness and others, and a rear portion of such a U-shaped pipe member is placed beneath a front region of a floor tunnel, which causes a problem that layout flexibility of members to be placed inside the floor tunnel is impaired. Moreover, in this vehicle suspension apparatus, it is difficult to facilitate deformation in a front portion of the U-shaped pipe member during a vehicle collision, so that it is unable to sufficiently bring out a collision load absorbing function based on compressive deformation of the front portion of the U-shaped pipe member.
The vehicle lower body structure disclosed in the Patent Document 2 is configured to receive a collision load input into a power plant in the event of a vehicle frontal collision, by three load-receiving points provided in a collision load transfer member, so that it has an advantage of being able to support the load by the plurality of front and rear frameworks of the lower portion of the vehicle body in a distributed manner, without generating an unexpected turning force in the power plant. However, when this vehicle lower body structure is applied to a vehicle in which a floor tunnel is formed in a bottom of a passenger compartment, a rear portion (rear-side cross beam) of the front subframe is also placed beneath a front end of a floor tunnel, which causes a problem that layout flexibility of members to be installed within the floor tunnel is impaired, and a vehicle body rigidity against an external force, such as a lateral force input from the suspension arm during vehicle traveling, cannot be satisfactorily ensured. In this regard, there remains a need for improvement.
The vehicle front body structure disclosed in the Patent Document 3 is configured such that, when the vehicle undergoes a frontal collision against an obstacle having a height lower than a front end of the vehicle-body frame, a collision load is transferred from the front subframe to the mounting portion and supported by the stopper portion, wherein the collision load is reliably received by the branch site between the floor frame and the branch frame provided to extend in the front-rear direction of the vehicle, or the stopper portion provided in the vicinity of the branch site. That is, this vehicle front body structure is capable of supporting the collision load while distributing it to the branch frame and the floor frame, to thereby prevent a rearward movement of the front subframe.
However, in the vehicle front body structure disclosed in the Patent Document 3, the front subframe comprises: a pair of right and left side members each having, in top plan view, a front portion placed to linearly extend in the front-rear direction of the vehicle, a bent portion located rearward of the front portion and bent inwardly in a vehicle width direction, a rear portion disposed rearward of the bent portion to extend in the front-rear direction, and a cross member placed to couple together rear ends of the right and left side members, wherein the front subframe is formed as a perimeter frame obtained by superimposing and joining an upper panel and a lower panel together, and a base end of a suspension arm (lower arm) is pivotally supported by the bent portion and the rear portion of the front side frame. For this reason, in this vehicle front body structure, the bent portion has to be largely bent inwardly in the vehicle width direction in order to satisfactorily ensure an arm length of the suspension arm to thereby improve suspension geometry. Thus, the front subframe has to be increased in size to satisfactorily ensure rigidity thereof, in order to configure the structure such that both a lateral force input from the suspension arm and a collision load input from a front end of the side member can be stably supported by the bent portion and the rear portion, which leads to negative effects, such as an increase in vehicle body weight, and occurrence of a situation where noise is likely to be generated due to panel vibration caused by an increased surface area of the front subframe.